The treatment of Crohn's Disease with biologics presents a number of challenges. Determining which patient population to study, predicting which subjects will respond to treatment, and which subjects will lose response following treatment are issues that have significant impact upon treatment and clinical study design. Biomarkers may be useful in answering these questions.
Biomarkers are defined as “a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention” (Biomarker Working Group, 2001). The definition of a biomarker has recently been further defined as proteins in which a change in the expression of may correlate with an increased risk of disease or progression, or predictive of a response of a disease to a given treatment.
Louis et al. (2002) used CRP (C-reactive protein) levels to identify which subjects with Crohn's Disease would response to the anti-TNFα antibody, infliximab. CRP levels in the responding subjects were significantly higher than in those subjects that did not respond to treatment. Schreiber et al. (2005) investigated the use of certolizumab pegol (a polyethylene-glycolated Fab′ fragment of anti-TNFα in Crohn's disease. They found that subjects could be stratified by CRP levels. Patients with CRP baseline levels greater than 10 mg/L showed a greater difference between active treatment and placebo due to a lower placebo response rate than those patients with CRP levels of less than 10 mg/L.
Sher et al. (1995) examined the expression of IL-1β, IL-2, IL-6 and IL-8 in the involved and uninvolved colonic segments of subjects with Crohn's Disease, as compared with normal colon. It was found that both IL-1β and IL-8 were expressed significantly higher in the diseased colon than the normal colon.
Kader et al. (2005) used protein microarray to examine the serum cytokine levels of pediatric patients with Crohn's Disease and ulcerative colitis. It was found that thirteen cytokines, when used together in a classification matrix, were able to distinguish active Crohn's Disease from disease in remission. The cytokines identified were BDNF, I309, IL-17, MCP-1, MPIF-1, PLGF, SCD23, TARC, TRAIL, UPAR, IL-12p40, IL-7, and TGFβ1.
Kucharzik T, et al (1995) found that IL-10 is elevated in serum of patients with active CD and UC, which suggested that IL-10 has role in the inflammatory processes of IBD. Bousvarous (1999) measured VEGF levels in children and adolescents with Crohn's Disease. It was found that VEGF levels were significantly higher in patients with Crohn's disease than in ulcerative colitis or control patients. The serum VEGF levels correlated with disease activity, with concentrations being elevated in patients with moderate or severe Crohn's disease and ulcerative colitis.
A review of the pathogenesis of inflammatory bowel disease (Dignass 2004) listed a number of cytokines that play a role in wound healing in the gastrointestinal tract. Lesions in the lining of the bowel characterize Crohn's Disease, and resolution of the disease by wound healing is of importance. Included in the list are cytokines that stimulate migration (TGFa, TGFb, EGF, FGF, IL-2) and inflammation (IL-1, TNFα, IL-6), and suppress inflammation (TGFβ, IL-4, IL-10).
In a recent study of the effect of anti-IL-12 (ABT-874; Mannon 2004), peripheral blood lymphocytes obtained from the nine study subjects before and after treatment were stimulated in vitro, and the release of cytokines by the lymphocytes measured by ELISA. The results showed that the secretion of IL-12, TNFα, IL-6, and interferon-γ were significantly reduced in the anti-IL12 treated subjects.
The studies cited above have utilized biomarkers to define the response of subjects with Crohn's Disease to infliximab and other biologics, or to classify patients according to the severity of their disease. In the paper related to Crohn's Disease and anti-IL-12, the biomarkers were expressed by cultured cells, but not detected in serum or plasma. To enhance clinical usefulness, the biomarkers are detected in serum or plasma.
Microarray technology is a powerful tool since it enables analysis of the expression of thousands of genes simultaneously and can also be automated allowing for a high-throughput format. In diseases associated with complex host functions, such as those known as immune mediated inflammatory diseases, such as Crohn's, microarray results can provide a gene expression profile that can be of utility in designing new approaches to disease diagnosis and management. These approaches also serve to identify novel genes and annotating genes of unknown function heretofore unassociated with the disease or condition.
Gene expression can be modulated in several different ways, including by the use of siRNAs, shRNAs, antisense molecules and DNAzymes. SiRNAs and shRNAs both work via the RNAi pathway and have been successfully used to suppress the expression of genes. RNAi was first discovered in worms and the phenomenon of gene silencing related to dsRNA was first reported in plants by Fire and Mello and is thought to be a way for plant cells to combat infection with RNA viruses. In this pathway, the long dsRNA viral product is processed into smaller fragments of 21-25 bp in length by a DICER-like enzyme and then the double-stranded molecule is unwound and loaded into the RNA induced silencing complex (RISC). A similar pathway has been identified in mammalian cells with the notable difference that the dsRNA molecules must be smaller than 30 bp in length in order to avoid the induction of the so-called interferon response, which is not gene specific and leads to the global shut down of protein synthesis in the cell.
Synthetic siRNAs have been successfully designed to selectively target a single gene and can be delivered to cells in vitro or in vivo. ShRNAs are the DNA equivalents of siRNA molecules and have the advantage of being incorporated into a cells' genome where they are replicated during every mitotic cycle.
DNAzymes have also been used to modulate gene expression. DNAzymes are catalytic DNA molecules that cleave single-stranded RNA. They are highly selective for the target RNA sequence and as such can be used to down-regulate specific genes through targeting of the messenger RNA.
Accordingly, there is a need to identify and characterize new gene markers relevant from serum or plasma useful in developing methods for diagnosing and treating immune-mediated inflammatory disorders, such as Crohn's disease, as well as other diseases and conditions, and a method for predicting how a patient would respond to a therapeutic intervention.